1. Field of the Invention
The invention relates to a fuel injection nozzle, which is provided with a nozzle body, a nozzle needle displaceable in the nozzle body, and two groups of injection ports. Depending on the magnitude of the opening stroke of the nozzle needle, either only one group of injection ports or both groups of injection ports are used for the injection. In this way, different injection cross sections can be employed, so that the fuel injection can be adapted better to the existing operating conditions of the internal combustion engine that is supplied by the injection system.
2. Description of the Prior Art
To enable selecting the injection cross section as desired, the opening stroke of the nozzle needle must be controlled as precisely as possible. By now, various attempted solutions to this problem exist. One possibility of controlling the opening stroke is to bring about the opening and closing of the nozzle needle directly by a piezoelectric actuator. In this way, virtually any arbitrary intermediate position within the needle stroke can be approached and maintained. Another possibility for controlling the opening stroke is to control the fuel pressure, which brings about the opening of the nozzle needle, in such a way that the desired opening stroke is established.
An object of the invention is to create a fuel injection nozzle in which the opening stroke of the nozzle needle can be limited to a desired value at little effort or expense and with high reliability. Another object of the invention is to create a fuel injection nozzle in which the injection cross section can be selected independently of all other parameters.
An injection nozzle according to the invention has the advantage that the opening stroke of the nozzle needle can be limited in the desired way at little effort or expense. If only a slight opening stroke is desired, then the control valve is closed, so that the fluid present in the stop chamber is prevented from flowing out. The control valve that controls the outlet from the stop chamber can be actuated with only little energy, since it is not acted upon directly by the high pressure that causes the opening of the nozzle needle. The control valve can also be actuated during the intervals between injections by the injection nozzle, that is, between two successive injection cycles, so that the switching events take place in phases when only low pressure is imposed, and stringent requirements in terms of timing need not be made of the switching phases. By the switching event, that is, the opening and closure of the control valve between two injections, the length that the opening stroke should have is already defined prior to a nozzle needle stroke. In contrast to this, in the known systems, the opening stroke has to be interrupted at a certain instant, which is why stringent demands are made in terms of the timing precision of the switching event.